REvil is ransomware that locks you out but first exfiltrates your data. Then the attackers have 2 points of leverage, lock out which you may be able to circumvent with a safe backup process but that won't protect you from the release of your data. This gives the attacker 2 nites at the cherry when trying to convince you to pay.
Both "hacking" and stealing are illegal in most countries, but they're still completely different actions: one is taking a physical object from someone, the other is sending and receiving electrical pulses trough a wire.
You wouldn't call stealing and killing by the same word, either, even though both are illegal.
Since we're discussing word choices and definitions, I'd argue that it's not stealing either if the Hospital retained possession of the data. It might be better said that they "obtained without authorization" or "illegally obtained".
What makes "stealing" particularly bad is that the rightful owner no longer has possession of their property. That's not necessarily the case with data.
This sort of thing is why people need to stop thinking that the digital world is analogous to our analog one.
In digital, information wants to be free and many kinds of resources are effectively unlimited. There is no material scarcity. Therefore, theft, in the digital world, can't be the same as it is in our analog world.
To be fair, this also applies to copyright and peoples' foolish notion that they can protect data without a great amount of preventing otherwise normal "physiological" processes. (Ironically, rather than having a wake-up moment where people realize their folly, we've institutionalized these resource-scarcity regimes into resource-abundant versions in the digital world)
To summarize, info wants to be free, and since theft requires extra effort to deprive someone of what you stole, does that definition of theft really apply here? Or does it need to change given the context? And, as a secondary point, people like to think they can protect data but their brains are stuck in our analog, resource-scarce world